1. Field of the Invention
This invention relates to a porous product for abstracting dissolved ions from aqueous solutions, and more particularly concerns a porous product having an improved ability to selectively absorb anions.
2. Description of the Prior Art
U.S. patent application Ser. No. 07/395,535, filed Aug. 18, 1989 now U.S. Pat. No. 5,002,984 discloses an open celled product useful in selectively abstracting dissolved ions from aqueous solutions. The product is comprised of a regenerated cellulose sponge and a water insoluble polymer durably associated with the cellulose. The polymer is essentially a polyethyleneimine (PEI) that has been insolubilized by a polycarboxylic acid in a thermal curing step. The PEI contains primary, secondary and tertiary amine nitrogen atoms. The primary and secondary nitrogen atoms interact with the polycarboxylic acid to form amide bonds, thereby causing insolubilization of the PEI.
U.S. patent application Ser. No. 07/561,006, filed Jul. 31, 1990 pending discloses a particularly preferred small cuboid configuration of the sponge product having a uniform distribution of polymer throughout the sponge and providing improved characteristics during manufacture and use.
Although the aforesaid sponge product can selectively absorb cations and anions, there is a need for improved absorption performance for certain anions. For example, the following anions pose significant challenge for either economic or ecological reason: AuCN.sub.2.sup.-, the dissolved form of gold produced by cyanide leach operations, is generally sought to be scavenged from mine waste tailings; CrO.sub.4.sup.-2, chromate ion, is a toxic substance employed in preventing microbial growth in cooling tower water, its removal being troublesome; Ag(S.sub.2 O.sub.3).sub.2.sup.-3, generated by photographic fixer solutions containing thiosulfate, produces serious toxic contamination when discharged into surface waters; and UO.sub.4.sup.-2, produced in the course of uranium mining, causes radioactive contamination in ground waters.
It is accordingly an object of the present invention to provide a porous sponge product having improved affinity for anion species, particularly anion species containing a metal element.
It is another object of this invention to provide a product as in the foregoing object which employs a cellulosic sponge containing PEI that has been insolubilized by thermal interaction with a polycarboxylic acid.
It is a further object of the present invention to provide a product of the aforesaid nature comprised of small size cuboid sponge and amenable to easy production.
These objects and other objects and advantages of the invention will be apparent from the following description.